1. Field of the Invention
The present invention relates to a metal element inspection device and a metal element inspection method for a metal element which is one of the constituent components in a V-belt for a Continuously Variable Transmission (commonly referred to as a “CVT belt”).
2. Description of the Related Art
FIG. 6A is an outline view diagram of a CVT belt in conventional prior art. As shown in this diagram, a CVT belt 1 is constructed by assembling two laminated belts 2 containing a plurality of metal belts 2a (for example, a stack of about 12 endless layers) which are supported by thin trapezoidal layered elements 3 composed of a large number of metal elements 3a (for example, about 400 consecutive steel elements). For instance, as disclosed in Japanese Laid-Open (Kokai) Patent Application No. 2003-231053 titled “BARREL POLISHING METHOD AND BARREL POLISHING MEDIA”, etc.
FIG. 6B is an outline view diagram of a metal element 3a. Each of the metal elements 3a consists of a steel block (small piece of metal) punch processed from a metal plate and molded into a specified shape. The specified shape, for example, is similar to the physical form of the upper-half image of a human body. Specifically, a metal element 3a resembles a molded shape having a head portion 3b and a chest portion 3c, along with a neck portion 3d which connects between the head portion 3b and the chest portion 3c. A protrusion 3e (raised circular knurl) is formed in one direction of the surface side (front surface as seen in FIG. 6B) of the head portion 3b and a cavity 3f (circular indent) is formed in the same location on the opposite direction surface side (rear surface of drawing). Alignment of the metal elements 3a is accomplished by consecutively inserting the protrusion 3e into the cavity 3f of adjoining metal elements 3a. 
Two laminated belts 2 are inserted in the recessed parts 3g (belt grooves) containing an infinitesimal space clearance width “L” of about several millimeters (mm) formed between the head portion 3b and the chest portion 3c of the metal elements 3a, respectively.
Here, although the metal elements 3a as stated above are punch processed from a metal plate and molded, after punch processing, the metal elements 3a are subjected to polishing (generally, barrel polishing) for creating a surface finish. Barrel polishing is a known technique which places a grinding object (referred to as “work”: the metal elements 3a mentioned above) and an abradant material (media) in a container (barrel tumbler) and surface treatment for removal of burrs (rough edges), “R” attachments, etc. is performed by relative friction between the work and the media generated during movement of the barrel.
Apart from that, since the metal elements 3a have an infinitesimal space clearance width “L” of about several millimeters (mm) formed between the head portion 3b and the chest portion 3c, when the size of the media (abrasive compound mixture) exceeds the width “L” between the recessed parts 3g, the recessed parts 3g cannot be polished. Consequently, removal of burrs (deburring) and “R” attachments in these recessed parts 3g can not be carried out.
Therefore, media of different sizes are mixed together and used. A technique for performing entire surface finishing including the recessed parts 3g of the metal elements 3a is known (for example, the above-mentioned Japanese Patent Application No. 2003-231053).
In this conventional prior art, media of the size at least larger than “L” (hereinafter denoted as “large media”) and media of the size smaller than “L” (hereinafter denoted as “small media”) are mixed and used.
Large media can be used to perform surface finishing for other than the recessed parts 3g of the metal elements 3a. Small media can be used to perform surface finishing for the recessed parts 3g of the metal elements 3a. 
However, as mentioned above, media of different sizes are mixed and used. When surface finishing of the metal elements 3a is performed, the following disadvantage is caused.
Polishing of the recessed parts 3g of the metal elements 3a is performed when small media enter the inner part of these recessed parts 3g. However, when the size of small media conforms to or is very similar in size to the recessed parts 3g, small media become lodged and are retained in the recessed parts 3g. Thus, in such a condition, there is a disadvantage that some of the small media is carried intact to a subsequent process.
Furthermore, the same disadvantage is also caused when a crack, a chip, etc. generated in large media becomes an object the size of these separated parts which is equivalent to the above-mentioned small media (conforms to or very near the size of the recessed parts 3g).
FIG. 6C is an outline view diagram of a metal element 3a state containing lodged media. As shown in this drawing, in a state where media 4 (foreign matter) is lodged in a recessed part 3g, this situation becomes a hindrance when assembling the metal elements 3a which support the laminated belts 2. These components have to be examined for the existence of lodged media 4 by visual observation. Consequently, a visual inspection of a large quantity of the metal elements 3a which involves a few hundred components for each CVT belt is very troublesome, inefficient and demands considerable manpower. In addition, although the foreign matter (media 4) in FIG. 6C is portrayed resembling a circular shape, this illustration is for convenience of explanation. There may be not only circular shapes but also various shapes.